Atrial fibrillation (AF) is a complex arrhythmia with a variety of underlying molecular and structural mechanisms contributing to a vulnerable AF substrate. The complexity of AF substrate seems to be reflected in the characteristics of AF electrograms (EGMs), with AF EGM morphology in paroxysmal AF being different than in more persistent AF. However, the precise structural and functional mechanisms that lead to the formation of AF EGMs have not been well elucidated. The need for a better understanding of the mechanisms underlying AF EGM formation is heightened by several recent descriptions of regions of high-frequency activity during AF called complex fractionated atrial EGMs (CFAEs). Several recent reports suggest that ablation of CFAEs seems to increase AF ablation success.
In the setting of structural heart disease, specifically heart failure (HF), a variety of mechanisms (for example, changes in ion-channel expression and gap junction distribution, inflammation, oxidative stress, and a variety of structural changes) are thought to contribute to the creation of a vulnerable AF substrate. Of the structural changes that occur in the HF atrium, fibrosis is considered to be especially important in creating conditions conducive to the genesis and maintenance of AF. In more structurally normal hearts, other mechanisms (for example, heightened autonomic activity) are thought to play a more dominant role in the genesis of AF.
Traditional pharmacological therapies, as well as recently developed surgical and ablative procedures for AF have had variable success. Surgical and ablative approaches are empiric (anatomic) and do not assess and target patient-specific pathophysiologic derangements. Since the ectopic foci that contribute to AF frequently arise in the pulmonary veins (PVs) and posterior left atrium (PLA), current ablative or surgical procedures are focused on electrically isolating these regions from the rest of the left atrium. Success rates of these procedures have been reported to improve by adding additional ablation or surgical lesions in the atria and by targeting regions demonstrating complex atrial fractionated electrograms (CFAEs), but these are not consistent findings. Furthermore, this increase in success rates is accompanied by an increase in complications and a decrease in atrial transport/contractile function.
In view of the limitations of current ablation/surgical approaches, there is a long-felt need to better define the mechanisms underlying AF and to develop novel therapies that specifically target these mechanisms.